MCCF33095 查看數據表（PDF） - Motorola => Freescale
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MCCF33095 Datasheet PDF : 12 Pages
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MCCF33095 MC33095
Solder Paste Content
It is recommended that the solder paste consist of 10% tin,
88% lead, and 2% silver alloy. However, 95/3/2 compositions
have had successful results.
A rosin based flux, such as RMA (Rosin Mildly Activated)
manufactured by Dupont and having spherical particles of 45
to 75 microns, should be used. The tackiness of the solder
paste at room temperature helps to hold the flip–chip in place
during the pick and place operation. The use of flux:
1) Prevents excess oxidation during reflow.
2) Optimizes the flow of liquid solder through the stencil.
3) Smooths the surface by reducing surface tension, and
4) Enhances the normalization of surface tension upon
reflow causing the flip–chip bumps to effectively
auto–align themselves to substrate bump pads.
A solder mask can be used for applications requiring high
precision as shown in Figures 11a and 11b.
to some intermediate temperature point for annealing
purposes.
Figure 12. Reflow Oven Profile
Additional
Annealing
350
Profile
300
Standard
Profile
0
3
6
9
12
t, TIME (MINUTES)
Figure 11. Figure 11a. Before Reflow
ÉÉÉÉÉÉÉÉ Conductive
ÇÉÉÇÉÉÇÉÉÇÉÉÇÇ Pad
IC
Flip–Chip Bump
Flattened Pb/Sn
Solder Mask
Ceramic
Figure 11b. After Reflow
ÉÉÉÉ IC
ÉÉÉÉÉÉÉÉ Conductive
ÇÉÇÉÇÉÇÉÇÇ Pad
Flip–Chip Bump
Pb/Sn
Reflow
Solder Mask
Ceramic
Oven Profile
After the flip–chip is placed onto the bumped substrate, the
substrate and flip–chip are ready for reflow. Initially, the
flip–chip is heated to a peak temperature of around 300° to
350°C for five minutes. It is to be noted that the flip–chip
bumps have a higher melting temperature than the bumps on
the substrate. During assembly reflow, the substrate bumps
melt and create a substrate to flip–chip bump bond. After
reflow, the assembled part is cooled to room temperature or
The oven temperature profile is established primarily to
melt the solder while minimizing the alloying of the materials
and keeping the flux from boiling away. It should be noted that
when the flip–chip is placed onto the substrate, the material is
stressed in one direction or another. The use of flux helps to
reduce any surface stresses present. A reduction in the
surface stress enhances solder wetting which in turn aids in
the alignment of the flip–chip to the substrate. Poor solder
wetting will produce misalignment as well as inferior bond
strengths and reliability.
It is recommended that an inert atmosphere such as
nitrogen be used during the reflow process to prevent
oxidation.
Final Cleaning
The final cleaning involves removing the remaining flux
from the flip–chip assembly. Three possible methods of
removing flux are: ultrasonic cleaner, Terpene solvent and DI
water, or vapor degreaser. The flux manufacturer should be
able to recommend the proper type of vapor degreaser to be
used.
Test and Reliability
Both visual inspection and shear strength testing should
be performed on packaged flip–chip assemblies.
Solder reflow results that exhibit a grainy and dull
appearance produce inferior bond shear strengths. Inferior
bond shear strengths are visually recognizable by:
1) The presence of old or badly oxidized solder paste.
2) Insufficient amount of solderable material.
3) The contamination of bond pads with grease, oil, etc.
It should be mentioned that many contaminants are
transparent and not easily detectable by visual means.
MOTOROLA ANALOG IC DEVICE DATA
9
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